As disclosed in Japanese Laid-Open Patent Publication No. 2003-284057 (hereinafter referred to as “JP2003-284057A”), it has heretofore been customary for a vehicle periphery monitoring apparatus to detect an object such as a pedestrian or the like that may possibly collide with a vehicle, from images (a grayscale image and a binary image converted therefrom) of the periphery of the vehicle, which are captured by infrared cameras, and to provide information about the detected object to the driver of the vehicle.
The vehicle periphery monitoring apparatus disclosed in JP2003-284057A detects, as an object, a high-temperature area in images in the periphery of the vehicle, which are captured by a set of left and right infrared cameras (stereo cameras), and calculates the distance up to the object by determining a parallax of the object in the left and right images. In addition, the vehicle periphery monitoring apparatus detects an object, such as a pedestrian or the like that is likely to affect the travel of the vehicle, i.e., that may possibly collide with the vehicle, based on the direction in which the object moves and the position of the object, and issues a warning concerning the detected object (see paragraphs [0014] and [0018] of JP2003-284057A).
Japanese Patent No. 4267657 (hereinafter referred to as “JP4267657B”) discloses a vehicle periphery monitoring apparatus, which captures at least two images (two frames) of an object in the periphery of a vehicle at a predetermined time interval, using a single infrared camera mounted on the vehicle. If the size of a present image of the object changes from the size of a preceding image of the object, the change in size becomes greater as the relative speed between the object and the vehicle incorporating the vehicle periphery monitoring apparatus is higher. As the relative speed between the object and the vehicle is higher, an arrival time, which any object that is present in front of the vehicle takes to arrive at the vehicle, becomes shorter. Consequently, even though a single infrared camera is used, the vehicle periphery monitoring apparatus can monitor the periphery of the vehicle by estimating the arrival time from the rate of change between the sizes of images of the object that are captured at the predetermined time interval (see paragraphs [0006], [0007], and [0061] of JP4267657B).
Japanese Patent No. 4173901 (hereinafter referred to as “JP4173901B”) discloses a vehicle periphery monitoring apparatus, which detects animals other than people from among objects, because objects that are present in the periphery of a vehicle and that may possibly collide with the vehicle are not limited to pedestrians. Large animals such as deer or the like may also be present on the road and may collide with the vehicle (see paragraph [0006] of JP4173901B).